Flashcards in Practice Exam Deck (25)
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1
Which two types of molecular interactions are most important in stabilising the structure of the DNA double helix?
Hydrogen bonds an hydrophobic interactions
2
RNA structure:
-RNA consists of unbranches chains of nucleotides
- the phosphodiester links in RNA join the 5’ position of one nucleotide with the 3’ position of the adjacent nucleotide
- the bases in RNA are uracil, adenine, guanine, cytosine
- RNA is single stranded = relative amounts of purines and pyrimidines are not fixed
3
Restriction endonucleases =
Cut the phosphodiester bonds between adjacent nucleotides in DNA
4
Quinolones =
Inhibit DNA gyrase
5
Actinomycin D =
Inhibits transcription by binding to DNA
6
Cycloheximide =
Inhibits protein synthesis in eukaryotes
7
Chloramphenicol =
Binds to the prokaryotic 70s ribosome particle
8
Which amino acid is sulphur present in =
Cysteine and methionine
= only these form disulphide bonds
9
Km =
Michaelis constant = the substrate concentration which gives 50% of the maximal rate
10
In a lineweaver-burk plot :
Intersection on Y axis = 1/Vmax
Intersection on x axis = -1/Km
Gradient = Km/Vmax
11
Which amino acid is present at the active site of pancreatic ribonuclease and is involved in the catalysis of RNA hydrolysis ?
Histidine + lysine
12
What are the substrates of DNA polymerase enzymes ?
Template DNA
Primer with 3’-OH
Deoxynucleotide trisphosphates
Mg2+
13
What are the products of DNA polymerase enzymes?
Pyrophosphate
The growing strand is one nucleotide longer
14
How does DNA polymerase 1 differ from 3?
DNA polymerase 3 =
Faster
More processive
Lacks 5’ > 3’ exonuclease activity
Has multiple subunits
15
Differences between primase and DNA polymerase enzymes?
- primase makes RNA and doesn’t need primer
- DNA polymerase makes DNA and requires a primer
16
What role does 3’-OH on the ribose play in the polymerase reaction ?
Nucleophilic attack of the a-phosphorous of the incoming dNTP
17
Give two examples of posttranscriptional modification of RNA in bacteria -
Base modification in tRNA/rRNA
Ribose methylation in tRNA/rRNA
18
Which type of bacteria
RNA is not subject to processing ?
mRNA
19
Which enzyme synthesises mRNAs in eukaryotes?
RNA polymerase 2
20
What posttranscriptional modification occur at the ends of eukaryotic mRNAs ?
Capping at 5’ end
Tail addition at 3’ end
Cleavage prior to addition of tail
- happens in the nucleus
21
Splicing =
Excision of introns sequences from the mRNA primary transcript and joining of the exons
22
Low Km =
Higher affinity of an enzyme for its substrate
23
Competitive inhibitor effectors on…
Km increase
Vmax unchanged
24
Non competitive inhibitor effects on…
Km unchanged
Vmax decrease
25
